PARQUET-641: Instantiate stringstream only if needed in SerializedPageReader::NextPage
PARQUET-641: Instantiate stringstream only if needed in SerializedPageReader::NextPage

Small change but still some visible impact.

Author: Uwe L. Korn <uwelk@xhochy.com>

Closes #126 from xhochy/parquet-641 and squashes the following commits:

9902b0e [Uwe L. Korn] PARQUET-641: Instantiate stringstream only if needed in SerializedPageReader::NextPage

wesm/parquet-cpp,wesm/parquet-cpp,advancedxy/parquet-cpp,advancedxy/parquet-cpp,MaxRis/parquet-cpp,flode/parquet-cpp,itaiin/parquet-cpp,itaiin/parquet-cpp,majetideepak/parquet-cpp,apache/parquet-cpp,flode/parquet-cpp,wesm/parquet-cpp,MaxRis/parquet-cpp,wesm/parquet-cpp,wesm/parquet-cpp,apache/parquet-cpp,advancedxy/parquet-cpp,itaiin/parquet-cpp,MaxRis/parquet-cpp,itaiin/parquet-cpp,flode/parquet-cpp,majetideepak/parquet-cpp,advancedxy/parquet-cpp,flode/parquet-cpp,MaxRis/parquet-cpp,majetideepak/parquet-cpp,apache/parquet-cpp,flode/parquet-cpp,majetideepak/parquet-cpp,MaxRis/parquet-cpp,majetideepak/parquet-cpp,itaiin/parquet-cpp,apache/parquet-cpp,majetideepak/parquet-cpp,advancedxy/parquet-cpp,MaxRis/parquet-cpp,advancedxy/parquet-cpp,itaiin/parquet-cpp,wesm/parquet-cpp,apache/parquet-cpp,apache/parquet-cpp